In the three years since Abu Ghraib became an emblem for American brutality in the so-called War on Terror, there has been no shortage of theories seeking to explain the causes of prisoner abuse.

In February, Dr. William Holmes, assistant professor of medicine and epidemiology, waded into this lively debate with some actual data. In a study published in Military Medicine, Holmes, who is also an investigator at the Center for Health Equity Research and Promotion at the Philadelphia VA Medical Center, tried to assess tolerance for detainee abuse among American military veterans. He found that fewer than one-third of participants expressed “zero tolerance” for a scenario involving prisoners stripped naked and stacked in a pyramid, and about half indicated that detainee rape was at least somewhat acceptable.

Using a questionnaire designed to measure veteran’s attitudes about several scenarios drawn from real-life cases at Abu Ghraib, Holmes found that several factors influenced participants’ response. Men were between four and 20 times more tolerant of abuse than women, and all the veterans looked more favorably upon abuse ordered by a superior officer than that initiated by a soldier. Those results were in line with expectations, but another came as a complete surprise. When faced with a scenario in which a second soldier had gone on record as condemning abuse carried out by a peer, the whistle-blowing dynamic actually seemed to make participants more tolerant of torture.

Soldiers form intense bonds within their unitsespecially in combat zonesand they inhabit a military culture that strongly discourages dissent. It may be that any action which betrays this solidarity “runs so morally counter to what is believed to be appropriate,” Holmes theorizes, “that something that would otherwise be seen as morally inappropriate as well becomes less so in the framework of having a whistleblower.” A lone voice of conscience may attract enough disgust to make a perpetrator of abuse seem defensible by comparison.

The study also found that regardless of the specific scenario participants were confronted with, veterans with clinical depression were twice as likely to be tolerant of detainee abuseand three times as likely if they also suffered from post-traumatic stress disorder (PTSD). If these results are replicated in active-duty soldiers, whom Holmes hopes to study next, it’s possible that similar scenario-based questionnaires could be used to determine their fitness for highly sensitive positions.

“If you saw tolerance trending upwards or downwards,” he says, “or you could identify that certain risk factors were occurringlike people developing depression or PTSDmaybe you could relieve them from that sort of duty.”

Yet the realities of war zones and prison situations would seem to suggest that such changes are unlikely. Holmes stresses that tolerance for torture does not always translate into action, but reasons that it is certainly a prerequisite. When you have “people on multiple rounds of traumatic service, and separation from family and normal society, and higher rates of depression,” he speculates, “there’s going to be increased tolerance [for abuse]. And then if you superimpose on that a top-down, constant barrage of discussion on what exactly torture is defined to be, then I think it makes this whole dynamic much more rich with the possibility that this behavior can happen.”T.P.